" a calculator "
ometa Calc {
  digit   ::= <char>:c ?[c isDigit]        => [c digitValue].
  number  ::= <number>:n <digit>:d         => [n * 10 + d]
            | <digit>.
  priExpr ::= <number>
            | "(" <expr>:e ")"             => [e].
  mulExpr ::= <mulExpr>:x "*" <priExpr>:y  => [x * y]
            | <mulExpr>:x "/" <priExpr>:y  => [x / y]
            | <priExpr>.
  addExpr ::= <addExpr>:x "+" <mulExpr>:y  => [x + y]
            | <addExpr>:x "-" <mulExpr>:y  => [x - y]
            | <mulExpr>.
  expr    ::= <addExpr>.
}.
Calc matchAll : '12-(34+2)*2' with: #expr